I'd still recommend doing searches for common spam topics to see if you have "bad" stuff. On our wiki everything looked fine until you searched for (say) "finance" (which most users never would) ... and then you'd find a mess of spam finance stuff.

As for whether it's responsible or not, obviously I don't know. What I do know is that, without all the info, "Google saw malicious content on your wiki" is a far more logical theory than "Google just decided to hate us out of the blue".